1. Technical Field
This invention relates to cordless telephones and more particularly to a cordless telephone employing a computer for providing increased functionality and for extending the useful battery life of such telephone.
2. Description of the Prior Art
A typical cordless telephone system includes a handset or remote unit and a base unit. The base unit is connected to the telephone lines and includes an antenna, a transmitter and a receiver for communicating a radio frequency carrier signal that is modulated by switching signals and audio signals to and from the handset unit as appropriate. Power for operation of the base unit is obtained from local line power. The handset unit includes a speaker and a microphone, and also an antenna, a transmitter and a receiver for likewise communicating telephone switching signals and audio signals to and from the base unit. Power for operation of the handset unit is obtained from a battery contained therein. This battery is usually charged by the local line power when the handset unit is placed in a cradle located in the base unit.
In the operation of a typical cordless telephone handset unit in originating and receiving a call, the receiver of the handset unit normally remains in a oncondition whenever the handset unit is removed from the base unit. If a user desires to place a call from the handset unit, the transmitter in the handset unit generates a control signal that is transmitted to the base unit. Upon receipt and detection of the control signal, the base unit seizes the telephone lines so as to enable audio signals and switching signals from the handset unit that are received by the base unit within a given audio frequency band to be passed onto the telephone lines. If an incoming telephone ringing signal is sensed by the base unit, reflecting an incoming call, the base unit, in turn, transmits this ringing signal to the handset unit where it is detected by the handset unit receiver which activates a ringer in the handset unit.
High battery drain current limits the period of time for reliable operation of handset units while located remote from associated base units. In order to extend this time and yet insure reliable operation for an extended period, some arrangements in the known art have resorted to installing an auxiliary or paging type ringer extension associated with the base unit or another part of the local telephone station where local line power is available. Thus when an incoming telephone ringing signal is noted on the ringer extension, the user of the handset unit activates the power-on switch of the handset unit and answers the telephone call remotely. Once the telephone conversation is over, the user shuts off the handset unit to conserve power once again. In this type of arrangement, however, the user must always be within hearing range of the ringer extension.
In order to extend battery life in the handset unit of a cordless telephone, one specific arrangement disclosed in U. S. Pat. No. 4,039,760 and issued to L. D. Gregory et al. on Aug. 2, 1977, proposes turning off the transmitter in the handset unit when the telephone is not in use and the handset unit is on-hock, i.e., no telephone call is in progress. While monitoring for a telephone ring signal, battery power is conserved by reducing the on-time of the receiver and control circuitry in the handset unit. In this arrangement, a tone decoder in the handset unit detects an audio tone of 3 KHz that is transmitted by the base unit to the handset unit whenever a ringing signal is received by the base unit from the telephone line. Similarly, a tone decoder in the base unit detects an audio tone of 3 KHz that is transmitted from the handset unit to the base unit for initiating a call from the handset unit.
While this type of arrangement reduces power consumption in cordless telephone handset units and extends battery life, it is quite susceptible to radio frequency (RF) interference in communications between the handset unit and the base unit. In the handset unit, e.g., the receiver is activated by the reception of a modulated carrier and is, therefore, subject to false activation signals possibly due to other cordless telephones in its reception range transmitting a modulated carrier on the frequency to which the receiver is then tuned, or any source of noise occurring at this carrier frequency. In communications from the base unit to the handset unit, the arrangement also does not allow for functionality other than the base unit providing a ringing signal to the handset unit.
Other disadvantages are known to exist with this specific arrangement. In communications from the handset unit to the base unit, access to the base unit is provided in the arrangement by the handset unit transmitting the modulated carrier signal. Other handset units belonging to other cordless telephone owners in the reception range of the base unit will also be able to obtain access to the telephone line through this same base unit as long as the same modulated carrier signal is utilized. Other possible undesirable interactions may occur as base units respond to other base units and handset units respond to or are activated by other handset units within their common reception range.
While the foregoing type of arrangement in a cordless telephone system has been generally satisfactory in the past in those environments having few cordless telephones and few other sources of potential RF interference nearby that could affect the operation of this type of system, it is now technically feasible and desirable to provide a cordless telephone system that provides increased battery life along with greater functionality while remaining relatively inexpensive and easy to operate.